springs, and the moment of ignition will be retarded. When the motor is being started from rest the ignition gear will be in its most retarded position, thus avoiding all risk of back-firing. The governor is adapted from the crank-shaft expansion governor fitted to steam engines. The important point is to adjust the spring tension correctly.

To supply the current necessary for the production of the spark, primary or secondary batteries, magneto or dynamo electric machines, are used. Magneto machines are used without a coil if the low-tension system is employed with a make-and-break inside the cylinder, but they may be used in conjunction with an induction coil and the usual sparking plug. Dynamos are not much used in this country, but in America there are several

makes of cars which have both dynamo and storage batteries, which can be used alternately at the will of the driver. With this arrangement the secondary battery is always kept fully charged; an automatic cut-in and cutout is fitted so that the dynamo is only in circuit when running at its proper speed, when the battery is cut out. This system would seem to promise well, but the dynamo requires designing so that its output is fairly constant at varying speeds.

General Design.—The relative advantages of horizontal and vertical engines have been the subject of much discussion in the past, and the vertical engine has so far been more generally employed, in this country and in France and Germany. In America the preference seems to be for horizontal motors. Both designs have their good and bad points fairly evenly balanced, but the writer inclines to the horizontal engine. With a vertical engine the vibration is more evident. The direction of movement of the disturbing forces in a horizontal motor is all in line with the axis of the car, in which direction they can best be resisted, whereas with a vertical motor the disturbing forces have only the springs to resist them. It has been advanced that the cylinder of a horizontal motor will wear oval in a much shorter time than when vertical, the contention being that this wear is caused by the weight of the piston. It is very much to be doubted whether the weight of the piston has any influence on the wear. The chief factor is the pressure due to the angular thrust of the connecting rod, and this will be practically the same in both vertical and horizontal cylinders. On the question of lubrication of the piston, it would seem reasonable to suppose that when this is effected by "splash" only, the vertical position will be best, but when the oil is introduced through the side of the cylinder, the horizontal position will secure better distribution.

To avoid forming shoulders in the cylinder bore by the wear of the piston, it is usual to allow the piston to move a short distance beyond the actual bored length by enlarging the diameter of the cylinder at the combustion chamber, and bell-mouthing the open end. The change in diameter at the combustion chamber should not be

abruptly made by stepping, but the surface should be tapered from one diameter to the other. If made by an abrupt step, and the piston should be pushed too far up the bore, one, or more, of the piston rings will spring out into the combustion chamber, and will prevent the piston being removed without breaking either it or the ring. If

the bore is tapered, however, the piston can be withdrawn without much difficulty, as the taper will act to close the ring back into its groove.

With any piece of machinery it looks bad to see the nuts overhanging the facings upon which they bear, or to see too great a surface of the facing showing round the For some time the writer has used the following standard dimensions where studs or bolts have been required in a design, and has found a considerable saving in time thereby. The dimensions given for the boss into which the stud is screwed apply more particularly to cases where it is not advisable for the end of the stud or screw to come right through, such as a cylinder waterjacket.

In all cases where two parts of an engine are bolted together, and where the edges of the parts are not machined, such as the cylinder and crank chamber, the upper piece should be slightly smaller than the lower, to give a little freedom in placing the parts while avoiding overhang. This applies specially to pipe flanges; there should always be from a sixteenth to an eighth of an inch of the facing showing all round the edge of the flange, unless the edges of both flange and facing are machined flush with each other.

The two following tables of flange dimensions will be useful in designing motors, Fig. 23 being for ordinary wrought-iron gas-pipe sizes, the pipe being screwed into the flange; and Fig. 24 for brass or copper tube, brazed into the flange. The dimensions in Fig. 24 might also be adopted where weldless steel tube of thin gauge, say up to No. 16 B.W.G., is in question; for thicker gauge tubing use Fig. 23. Where it is necessary to employ coned unions, the dimensions in Fig. 25 can be followed. The ordinary coned unions used for connecting up gaspiping will generally require regrinding, with a very fine